The present invention is directed to rack-level and cage-level environmental monitoring and control in a ventilated cage and rack system.
It is well-known in the art to house laboratory animals, such as mice and rats, in cages. It is also well-known in the art to house the cages on racks. These cages are typically ventilated and, when placed in a rack, environmentally controlled (e.g., air-flow and air-exchange rate) by a fan system of the rack. In general, the rack fan system provides air under pressure to each of the cages within the rack, and exhausts air from the cages and the rack, as is known in the art.
While prior art ventilated cage and rack systems have been satisfactory, the air within the cage must be changed, or refreshed, on a periodic basis to prevent ammonia build-up, humidity build-up, carbon monoxide build-up, or the build-up of other potentially harmful gases, which may have an adverse effect on the animal within the cage. Changes in temperature in the cage and rack system must also be monitored and controlled to protect the animals housed in the cages. Although the prior art ventilated cage and rack systems did put the cages under positive pressure to create air flow through the cage, those systems do not have the capability to monitor and maintain the desired air flow within the cage and rack or to otherwise monitor and control the environment in the cage and rack. Typically, the supply air system is set for a predetermined air flow rate into the rack, and the exhaust air system is set at a maximum air flow rate. Such a configuration does not adjust air flow into and out of the system as the input and exhaust filters clog, which always occurs. Thus, current rack and cage ventilation systems cannot provide rack and/or cage-level control of the environment in the rack and/or cages. There thus exists a need in the art for a system for monitoring and controlling the air flow within the rack and to the cage at both the rack level and cage level.
The present invention is directed to an environmental monitoring and controlling system for a ventilated cage and rack system. The present invention monitors and measures air flow in the rack at either the rack or cage level. At the rack level, two pressure zones are created in the air flow that provide a means to accurately measure the flow rate into the rack. The two zones are created in such a way as to minimize the energy loss of the flow. At the cage level, a specially designed Venturi used in conjunction with a heated thermistor bead accurately measures the flow rate into an individual cage and to monitor the air flow rate in a cage located at any cage position in the rack. The method of measuring the flow in this case differs from that of the rack due the fact the flow is on the order of being 100 times less. For example, the cage may be located in a position known to experience the lowest air change per hour rate. Control of the supply air system may thus be effected by the cage and determined by the air flow rate (i.e., air change per hour rate) detected at the cage level. Control of air flow into the rack, whether at the rack-level or cage-level is accomplished by comparing measured air flow data (measured at the supply or cage) with a desired air flow rate (which translates to a desired air exchange rate for the rack and/or cage). Based on that comparison, the operation of the supply air system, namely, the rotational speed of the fan, is controlled so as to achieve the desired air flow rate. Similarly, the exhaust air system monitors and measures the exhaust air flow rate and compares that rate against a predetermined exhaust air flow rate. Operation of the exhaust air system is adjusted so as to provided that desired exhaust air flow rate.
In a first embodiment of the present invention, a system for monitoring and controlling the rack-level environment includes a supply air system for detecting and controlling the air flow rate into the rack, and an exhaust air system for detecting and controlling the air flow rate out of the rack. Each of the supply air system and exhaust air system are similarly constructed, and include a Venturi housing having an air channel defined therethrough. For the supply air system, a first section of the Venturi housing has a larger diameter than a second section, with the second section constricting air flow through the air channel and causing an increase in the velocity of air flow through the Venturi housing. A first pressure zone (detector) is provided in the first section, and a second pressure zone (detector) is provided in the second section. That placement of the two pressure zones, together with the use of a Venturi housing, enables an accurate determination of the air flow rate (which is directly related to the air exchange rate of the rack) using inexpensive pressure detectors. In a preferred embodiment, the pressure zones are apertures in the housing connected to a differential pressure circuit via two tubes. That circuit receives pressure data from the pressure zones and determines a difference between two pressures, which provides an accurate indication of the air flow rate (and air exchange rate) in the rack. The differential pressure circuit provides a signal indicating the air flow rate to a microcontroller circuit, which provides a signal to a fan interface circuit that controls the rotational speed of a fan located at the input of the Venturi housing and which controls air flow into the system.
In a similar manner, the exhaust air system includes a Venturi housing having two pressure zones provided in the air flow path for detecting air pressure at two points along that path. The detected pressures are again provided to a differential pressure circuit, which provides a signal indicating the air flow rate through the exhaust air system to a microcontroller circuit, which provides a signal to a fan interface circuit that controls the rotational speed of a fan located at the output of the Venturi housing and which controls air flow out of the system.
In another embodiment of the present invention, rack-level environmental monitoring and control is provided only by a supply air system, as described above and in more detail below.
In yet another embodiment of the present invention, cage-level environmental monitoring and control are provided. A Venturi tube is provided in a dummy cage (i.e., one that is not used to house an animal) and coupled to a controller that monitors the air flow rate through the Venturi tube (using a thermistor), and provides feedback to a rack-level control system to control the supply air system and, in effect, air flow at the cage level.
The present invention accordingly comprises the features of construction, combination of elements, arrangement of parts, which will be exemplified in the disclosure herein, and the scope of the present invention will be indicated in the claims.